This invention relates generally to systems for attachment to a subscriber's telephone, and more particularly to systems for intercepting incoming telephone calls and allowing only those calls authorized by the subscriber to be put through to the subscriber's telephone set.
Annoyance telephone calls are a common everyday experience in modern society. Salesmen, solicitors and others often call at inconvenient times such as the dinner hour or late at night when they know a subscriber will be at home. Most people would prefer not to receive such calls, however, because of the possibility that an incoming call may be of an emergency nature or may be an important message, the incoming call must be answered.
In order to reduce the number of unsolicited telephone calls, many people have requested unlisted telephone numbers. However, this results in increased costs to the telephone subscriber, while not being totally effective in preventing the reception of unwanted and annoying telephone calls. This is because solicitors and others can usually find out the telephone number of a subscriber through various means including the use of certain automatic sequential dialing machines.